1. Field of the Invention
The present invention relates to a method of manufacturing a thin-film magnetic head having at least an induction-type electromagnetic transducer.
2. Description of the Related Art
Recent years have seen significant improvements in the areal recording density of hard disk drives. In particular, areal recording densities of latest hard disk drives have reached 80 to 100 gigabytes per platter and are even exceeding that level. It is required to improve the performance of thin-film magnetic heads, accordingly.
Among the thin-film magnetic heads, widely used are composite thin-film magnetic heads made of a layered structure including a recording (write) head having an induction-type electromagnetic transducer for writing and a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading.
In general, the write head incorporates: a medium facing surface (an air bearing surface) that faces toward a recording medium; a bottom pole layer and a top pole layer that are magnetically coupled to each other and include magnetic pole portions opposed to each other and located in regions of the pole layers on a side of the medium facing surface; a recording gap layer provided between the magnetic pole portions of the top and bottom pole layers; and a thin-film coil at least part of which is disposed between the top and bottom pole layers and insulated from the top and bottom pole layers.
Higher track densities on a recording medium are essential to enhancing the recording density among the performances of the write head. To achieve this, it is required to implement the write head of a narrow track structure in which the track width, that is, the width of the two magnetic pole portions opposed to each other with the recording gap layer disposed in between, the width being taken in the medium facing surface, is reduced down to microns or the order of submicron. Semiconductor process techniques are utilized to achieve the write head having such a structure. In addition, many write heads have a trim structure to prevent an increase in the effective track width due to expansion of a magnetic flux generated in the pole portions in the medium facing surface. The trim structure is a configuration in which the pole portion of the top pole layer, the recording gap layer and a portion of the bottom pole layer have the same width taken in the medium facing surface. This structure is formed by etching the recording gap layer and the portion of the bottom pole layer, using the pole portion of the top pole layer as a mask.
One of the parameters that affect the writing characteristics of the thin-film magnetic head is the throat height. The throat height is the length (height) of the pole portions, that is, the portions of the two pole layers opposed to each other with the recording gap layer in between, as taken from the medium-facing-surface-side end to the other end. The throat height affects the intensity and distribution of the magnetic field generated near the recording gap layer in the medium facing surface. Therefore, it is required to control the throat height with accuracy to control the writing characteristics of the thin-film magnetic head with accuracy.
The throat height may be determined by forming a stepped portion in the bottom or top pole layer. If the throat height is determined by forming a stepped portion in the bottom pole layer, it is possible to form the top pole layer defining the track width on a flat surface and to form the pole portion of the top pole layer that is small in size with accuracy. Methods of determining the throat height by forming a stepped portion in the bottom pole layer are disclosed in, for example, the U.S. Pat. No. 6,259,583B1, the U.S. Pat. No. 6,400,525B1, and the U.S. Pat. No. 5,793,578.
Reference is now made to FIG. 21 and FIG. 22 to describe a typical method of forming the stepped portion for defining the throat height in the bottom pole layer. In this method, as shown in FIG. 21, an etching mask 102 is formed on a bottom pole layer 101, and the bottom pole layer 101 is selectively etched through the use of the mask 102 to form a groove 103 in the bottom pole layer 101. According to this method, it is difficult to form sidewalls 104 making up the groove 103 formed in the bottom pole layer 101 in such a manner that the sidewalls 104 are orthogonal to the top surface of the bottom pole layer 101. In particular, the surfaces of portions 104a of the sidewalls 104 close to the top surface of the bottom pole layer 101 form a greater angle with respect to the direction orthogonal to the top surface of the bottom pole layer 101.
A recording gap layer is formed on the bottom pole layer 101 that has been etched. In general, before the recording gap layer is formed, as shown in FIG. 22, the mask 102 is removed and then an insulating layer 106 is formed to cover the bottom pole layer 101. The insulating layer 106 is polished so that the bottom pole layer 101 is exposed to flatten the top surfaces of the bottom pole layer 101 and the insulating layer 106. The recording gap layer is formed on these flattened surfaces. In FIG. 22 numeral 107 indicates the level in which polishing is stopped.
According to such a conventional method, the surfaces of the portions 104a of the sidewalls 104 of the groove 103 close to the top surface of the bottom pole layer 101 form a greater angle with respect to the direction orthogonal to the top surface of the bottom pole layer 101, as described above. As a result, the method has a problem that the throat height greatly varies depending on the level in which polishing is stopped.